Climate, Marine West Coast

Marine west coast climates are located in the mid-latitudes, usually on the west coast of continents along the Atlantic Ocean and Pacific Ocean. Specifically, marine west coast climates exist in Europe from northern Spain to southern Norway, including the British Isles, the west coast of North American from California to Alaska, and the southern coast of Chile in South America. Other locations include the east coast of South Africa, the southeast coast of Australia, and the islands of New Zealand and Tasmania. Major world cities located in marine west coast climates include Seattle, Vancouver, London, Paris, and Berlin.

Marine west coast climates have relatively cool, mild temperatures and receive frequent precipitation most of the year. Marine west coast climates include frequent precipitation and overcast skies, due to the proximity of these climates to the ocean and semipermanent low-pressure areas. These low-pressure areas include the Aleutian Low of the North Pacific and the Icelandic Low of the North Atlantic. The low-pressure areas are most intense in the winter and are the origin of mid-latitude storms traveling eastward. In the Southern Hemisphere, the marine west coast climates are also located in the direct path of eastward-moving, mid-latitude storms.

A key characteristic of marine west coast climates is the moderating effect the ocean has on air temperature. Frequent cloudiness and overcast skies also moderate temperatures. In the summer, daytime maximum temperatures range from 15–25 degrees C (59–77 degrees F) and nighttime temperatures are usually 10–15 degrees C (50–59 degrees F).

Winters are mild; however, more poleward marine climates have colder winter temperatures and heavy winter snow. Depending on location, winter daytime temperatures may range from −4 to 10 degrees C (25–50 degrees F), and nighttime temperatures can range from −9 to 4 degrees C (15–40 degrees F). The warmest marine west coast climates are in South Africa and Australia, where freezing temperatures are rare. The coldest marine west coast climates are in southern Alaska and southern Norway, where winter temperatures are below freezing. In marine west coast climates, precipitation is more evenly distributed throughout the year than in neighboring Mediterranean climates. Some marine climate locations receive significantly high annual precipitation. For example, Dublin, Ireland, on average receives about 730 millimeters (29 inches) of precipitation annually, while Quillayute, Washington, receives about 2,600 millimeters (102 inches). Most marine west coast climates are wet; however, the variance in actual precipitation relates to the orographic features, which promote increased precipitation on their windward side and decreased precipitation on the leeward side.

Provided there are good, nutrient-rich soils and a sufficient growing season, many marine west coast climates are suited for agriculture. The natural vegetation biome types commonly occurring in west coast climates include deciduous, mixed, and evergreen forests. The coolest marine west coast climates such as those found in Norway and Iceland consist of subarctic-type grasses, sedges, and are treeless in some locations. The wettest marine west coast climates in the U.S., Canadian, and New Zealand west coasts have temperate rainforests with evergreen conifers and dense vegetation over the forest floor.